In the prior art, ink has been transferred from the fountain to the image plate by transferring ink from one roller to another along a roller train. Initially the ink is passed from the fountain to a fountain roller and the thickness of the ink applied to the fountain roller is determined by the gap between a single fountain blade, or a segmented fountain blade, and the fountain roller. As is well understood in the prior art, there is a plurality of keys, or screws, located on the underside of the fountain blade. The keys come in contact with the fountain blade at different height settings thereby providing different gap thicknesses between the fountain blade and the fountain roller, along the length of the fountain blade. The different gap thicknesses, of course, provide for different amounts of ink to be applied to the fountain roller, along the length of the fountain roller. The different amounts of ink being applied to the fountain roller accommodate the different dimensions of the areas to be inked on the image plate. In the prior art, a ductor roller is employed to initially lift ink from the relatively slow speed fountain roller. Thereafter, the ductor roller is physically moved to transfer the ink, that it has received from the fountain roller, onto a high speed receiver roller, in batches. As the ink is transferred from the receiver roller and thereafter from one roller to another in the roller train, the batches are smoothed out until finally ink is transferred to a form roller which functions to apply the ink to the image plate.
The above described method of transferring ink from the reservoir to the image plate has several disadvantages. Continuous blades, as opposed to segmented blades, are difficult to adjust because the more flexible the blade the more localized is the effect of the key and the more likely that the hydrodynamic pressure of the ink in the gap will push the blade away from the fountain roller in the areas between the keys. While rigid blades reduce the bowing of the fountain blade between keys, such rigid blades make it difficult to obtain an ink fed profile that enables widely diverse ink feeds to correspond to the needs of the plate image distribution. Segmented blades have been developed to counter the problems related to continuous blades as set forth above. However segmented blades have their own problems which result because ink and solvents get between the segments and cause mechanical malfunctions. In some prior art systems, which use segmented blades, a plastic shield has been located between the segmented mechanism and the fountain roller but such a shield has incurred wear problems causing the gap to change with time and use.
All of the foregoing prior art systems suffer from a serious problem related to effecting a precision setting of the ink gap particularly when the system requires low settings. For instance, assume that the image plate is comprised of a large area on one side of the plate to be inked, while the other side has a small postage stamp sized area to be inked. The dwell, or the sweep, of the ductor roller on the ink fountain roller must be adequate to allow a practical opening (perhaps an opening of 0.015 inches) of the keys which lie opposite the large area to be inked. On the light coverage side the ink gap would likely be held down to perhaps 0.001 inches or less. It may be that the run-out of the fountain roller may be 0.001 inches and there would be bowing of the roller and fountain blade from the hydrodynamic pressure of the ink. The hydrodynamic pressure, in turn, will vary with the speed of the press. It can be readily seen from the foregoing conditions that problems do result if the user does attempt to preset the fountain blade gap to accommodate different demands for ink on the image plate. Another set of problems results, in the prior art systems, from the inability to set a zone to a zero feed. When no feed is required, i.e., at the non-printing areas of the plate, the key closure can wear and bow the fountain roller thereby affecting other key settings.
Still another problem, that is inherent in the prior art arrangement, is the problem of the varying momentum of the ductor roller. The ductor roller in the prior art alternately runs in contact with the high surface speed of the receiver roller and then runs in contact with the relatively slow speed of the fountain roller. When the ductor roller leaves the receiver roller it is spinning at a very high speed and as it comes in contact with the fountain roller it skids due to the deceleration it experiences in adapting to the slow speed of the fountain roller. Such skidding results in an initial non-predictable transfer of ink. The transfer of ink is different during the early contact between the fountain roller and the ductor roller from that which takes place when the two rollers, i.e., the fountain roller and the ductor roller, are rolling together at the same speed. In the present system, the fountain gap is maintained at a relatively fixed width and thereby many of the above mentioned problems are eliminated.